This invention relates in general to an absorptiometer and in particular to a high sensitivity absorptiometer which is especially suited for detecting a component contained in a sample to be detected with a high detection sensitivity.
In these years great progress has been made in the field of absorptiometer and there are available various high sensitivity absorptiometer with a low noise and reduced drift. Such reduced noise and drift characteristics have been accomplished to a certain degree through attempts for developing a stabilized electric power source for a light source and improving a signal processing system such as electronic amplifier circuits or the like. However, there are demand for an absorptiometer with a more enhanced sensitivity, as an increased accuracy is required in the measurement and analysis in the associated field such as liquid chromatography.
Ammong the causes for the generation of noise and drift which can not be eliminated by electric or electronic circuitries, there may be enumerated a movement or flow of a sample in the application where the sample containing or accommodating means is composed of a flow cell. It has, however, been found that there still exist other causes for the noise and the drift, even after the problem due to the sample flow has been solved.
In this connection, it is to be noted that the light source chamber as well as the sample containing means chamber of the hitherto known absorptiometer are opened to the exterior with a view to obtaining a good ventilation. In general, the light emitting source of the absorptiometer will at the same time constitute a heat generating source. Accordingly, when the light emitting source is exposed to the atmosphere, ambient air around the light source will be thermally expanded due to the thermal conduction, radiation and convection of heat generated by the hight source. Such movement of air of course involves additional air flow and gives rise to irregular movements of air, i.e. a so-called air turburence phonomenon.
The inventors of the present application have found in the course of study for developing a high sensitivity absorptiometer that occurrence of the air turbulence or movements in the optical system of the absorptiometer will cause light beams passing there through to be refracted irregularly thereby to bring about changes in the light quantity impinging onto the photo-detector, which in turn provides a cause for the noise and the drift of the detected signals. Heretofore, no report has been made on such adverse influence of air movement or turbulence phenomenon.